GB 2253420B describes a process whereby an assembly of fibres of an oriented polymer may be hot compacted to form a sheet having good mechanical properties. The process involves an initial processing step in which the fibres are brought to and held at the compaction temperature whilst subject to a pressure sufficient to maintain the fibres in contact, the contact pressure, and thereafter compacted at a higher pressure for a few seconds, the compaction pressure. In the process a proportion of the fibre surfaces—most preferably from 5 to 10% by weight—melts and subsequently recrystallises on cooling. This recrystallised phase binds the fibres together. Preferred materials for use in this process are homo- and co-polymers of polyethylene.
The process of GB 2253420B can be used to produce complicated and precisely shaped monolithic articles having high stiffness and strength, and good energy-absorbing properties. However, a drawback of this process is the criticality of the compaction temperature, especially for polyethylene. This is shown by Comparative Example A in GB 2253420B.